The present invention relates to a fuel injection control system for a two-cycle engine having an electronic control system such as a microcomputer.
The fuel injection control system having the microcomputer is widely used in a four-cycle engine.
A recent two-cycle engine is also equipped with an electronic control system for controlling various components of the engine, such as fuel injectors. Japanese Patent Application Laid-Open 63-255543 discloses such an electronic fuel injection control system for the engine. The system has a main intake pipe for inducing fresh air to a crankcase and a sub intake pipe for directly inducing fresh air to the crankcase. A fuel injector is provided in each of the intake pipes. An electronic control unit is provided for controlling the injection timing and quantity of fuel injected from the fuel injector.
Japanese Patent Application Laid-Open 63-29039 discloses a system in which the quantity of intake air Q is derived from a look-up table in accordance with throttle valve opening degree .alpha. and engine speed N as parameters for calculating a basic fuel injection quantity Tp. Fuel injection quantity is calculated by correcting the basic fuel injection quantity with various correcting quantities in accordance with engine operating conditions. Coolant temperature, intake air temperature and atmospheric pressure are usually used as parameters for determining the engine operating conditions.
In the two-cycle engine, the intake air is induced in a crankcase and compressed before being transferred to a combustion chamber. Thus the charging efficiency of the engine is affected by the temperature of the crankcase. Namely, the charging efficiency decrease with an increase of the crankcase temperature.
On the other hand, a snowmobile, on which the two-cycle engine is mounted, is driven under various ambient conditions, so that the temperature of the crankcase decrease to about -50.degree. and increase up to 100.degree. C. Therefore, coolant temperature does not accurately represent the crankcase temperature so that an optimum air-fuel ratio cannot be obtained.
Moreover, if the quantity of fuel to injected is determined irrespective of the crankcase temperature, when the engine is restarted a large quantity of fuel is injected. Although the engine is already warmed up, thereby excessively enriching the air-fuel mixture. Hence the engine cannot be properly started.